In household appliances it is generally necessary to dry the items to be treated. This is the case, for example, with washer driers and laundry driers as well as in particular in dishwashers. It is known that a dishwasher has a washing process whose program sequence normally consists of at least one pre-rinse partial program step, one clean partial program step, at least one intermediate rinse partial program step, a clear rinse partial program step and a drying partial program step. To enhance the cleaning effect, the washing liquid is heated before or during a partial program step. The washing liquid is usually heated by means of an electrical heater. Various drying systems are known for drying washed items, i.e. crockery, in a dishwasher.
In a dishwasher, for example, the crockery or washed items can be dried by own-heat drying if the washing liquid is heated in a partial program step clear rinse and thus the washed items which have undergone a hot clear rinse are dried by themselves by the self-heat of said washed items which has thus built up during the following drying partial program step. In order to achieve this own-heat drying, the washing liquid is heated to a certain temperature in the clear rinse partial program step and applied to the washed items by means of spraying devices. As a result of the relatively high temperature, usually 65-75° C., of the washing liquid in the clear rinse partial program step, it is achieved that a sufficiently large quantity of heat is transferred to the washed items so that water adhering to said washed items vaporises as a result of the heat stored in said washed items. A disadvantage however is that the strong heating both of the washing liquid and also the washed items to high temperatures requires a very large amount of energy.
A method for operating a dishwasher is known from DE 30 21 746 A1 of the applicant, wherein a heat exchanger connected to the washing container in a heat-conducting manner is supplied with cold fresh water during a drying partial program step. A condensing surface is thereby produced on the inside of the washing container on which moisture condenses and the condensation formed remains in the washing container. Since the temperature difference between the moist air and the fresh water which is poured in, is relatively small, and the quantity of fresh water is heated continuously, this results in the disadvantage that the condensation of the moist air lasts for a long time and continually becomes smaller. In addition, strong heating of the washed items and the washing liquid is required in a partial program step preceding the drying partial program step, in particular clear rinsing, which means a high energy expenditure.
In another drying method for dishwashers, the air saturated with water is circulated by a blower and heated by a heater. This takes place in particular in a channel in which the blower and an electrical resistance heater are arranged. Saturated air is sucked out from the washing container via an outlet and is blown into the washing container again via an inlet after heating. As a result of this strong heating of the air, this air can thus absorb more moisture from the air again, i.e. thereby dry the crockery. One possible means for condensation of the moisture in the air is disadvantageously only possible to a limited extent in this drying system. One possibility for condensation only exists at the walls of the washing container which are possibly in thermal contact with the ambient air. However, the walls of the washing container are likewise heated so that only a small temperature difference and therefore a low condensation capacity is provided. In addition, a heat exchanger can also be provided in this drying system with a blower on the washing container in order to slightly improve the condensation performance and thereby the drying result.
Dishwashers are also known in which the air enriched with moisture is blown outwards. This has the disadvantage that pieces of furniture, i.e. kitchen furniture, can be damaged by the escaping moisture. Dishwashers are also known which guide the moist air over condensing surfaces on which the moisture condenses before this moist air is released to the surroundings. This can minimise the risk of damage to items of furniture because a smaller amount of moisture from the dishwasher is released to the surroundings.
A condensing device for a household appliance and a method for operating the same is known from DE 198 13 924 A1. A Peltier element has a heat-emitting surface and a heat-absorbing surface. A heat-absorbing surface extracts heat from working chamber atmosphere of a working chamber of the household appliance with the result that moisture from the atmosphere of the working chamber condenses at the cooled location. In a dishwasher, the heat-absorbing surface is located either inside the washing container or outside the washing container on the outside of the washing container wall and is coupled thermally to said wall in order to absorb the thermal energy from the washing container by means of heat conduction through the washing container wall. The heat-emitting surface releases the heat to the ambient air or to a heat-absorbing volume, e.g. water. A filling body as well as additionally a fan can be arranged on the heat-emitting surface to increase the heat release to the ambient air. In addition, in a further embodiment, the heat-absorbing volume can also be flowing water which can be taken continuously from the fresh water supply. Thus, a disadvantage with this condensing device for a household appliance and the method for operating the same is that merely the heat-absorbing surface of the Peltier element is used to condense the water contained in the gas or vapour phase in the washing container atmosphere. The heat-emitting surface of the Peltier element can thus disadvantageously not be used to improve the drying performance in the washing container atmosphere.